Amplitude anomalies of reflections in seismic recordings have been used for many decades. Initially, the focus was the search for high-intensity seismic reflections, so-called bright spots, in stacked seismic sections. These bright spots could indicate hydrocarbon accumulations, particularly gas. An important development was the introduction of amplitude-versus offset (AVO) interpretation techniques, in which observations of reflection coefficients for different angles of incidence can be used to discriminate different lithologies. This allows the separation of gas- and non-gas-related amplitude anomalies.
Other applications of amplitude interpretation are the detection of oil reservoirs and of porosity in carbonates as described for example by Castagna et al. (Castagna & Backus, 1993, Offset-dependent reflectivity—Theory and practice of AVO analysis, Society of Exploration Geophysicists).
However, before amplitudes can be interpreted in recorded data, they require a compensation or removal of near-surface and acquisition-related effects, such as source strength and receiver coupling variations. These variations influence all common-midpoint (CMP) based processing, since traces with different sources and receivers are combined in a CMP stack. This degrades the quality of the stack and could lead to biased AVO trends, particularly when related to slowly varying near-surface conditions.
For seismic signals recording along more than one directions, so-called multi-component data, it is important to realize that acquisition-related perturbations distort the vector-wavefield characteristics, since coupling has a different effect on horizontal and vertical source and receiver components. This can bias the observed polarization, for example, in determining the polarization direction of the leading split shear wave involves simultaneous rotation of the horizontal source and receiver coordinates to conform to the principal axes of an azimuthally anisotropic medium. This determination can only be achieved after separating the acquisition-related amplitude effects on the different recorded wavefield components from the medium response effects.
Amplitude corrections can be performed using surface-consistent processing techniques as proposed by a variety of prior art documents including Taner & Koehler, 1981, Surface consistent corrections: Geophysics 46, 17-22; Levin, 1989, Surface-consistent deconvolution: Geophysics 54, 1123-1133; Cambois & Stoffa, 1992, Surface-consistent deconvolution in the log/Fourier domain: Geophysics 57, 823-840; and Cary & Lorentz, 1993, Four-component surface-consistent deconvolution: Geophysics 58, 383-392). The existing techniques are applicable to primary reflections which have to be isolated in the data, and common-depth point (CDP) gathering is assumed to be valid. The term “surface-consistent” refers to the following approximations: the source and receiver amplitude terms can be expressed as finite-impulse response filters which do not vary throughout the recording time and are independent of the direction of propagation of the incident wavefield.